Well in this trucks case its pretty much trail only. So a shackle rear design would work out ok. However you also have to keep in mind when going super flexy where the axle and where the tire will go durring the full cycle. A shackle rear design means that when stuffing the tire goes towards the firewall. Well it can only go but so far and you can only trim back there but so much. If the shackles are forward you have the axle move forward when stuffing and you can cut up there TONS. In otherwords with the shackles forward you can have far more uptravel on the explorer. Otherwise we would have had to push the super long wheelbase out even further.